A behavioral cascade: Top-predator induced behavioral shifts in planktivorous fish and zooplankton

It is well known that the effects of direct (lethal) predator-prey interactions propagate through food webs (the trophic cascade). However, in the present study we show for the first time that, parallel to the trophic cascade, there exists a behavioral cascade in the sense that behavioral responses, induced by the nonlethal presence of a top predator, are transmitted down the food chain over more than one trophic link. By using a new method, horizontal echo sounding, in an enclosure study in a shallow lake in southern Sweden, we recorded the swimming activity and refuge use of young-of-the-year (0+) roach (Rutilus rutilus) in the presence and the absence of a caged predatory fish. By connecting the predator avoidance behavior of 0+ roach with that of zooplankton throughout summer, we show that species interactions are more dynamic than had been predicted earlier by food web theory. In our study, 0+ roach changed their behavior by becoming less active in early summer and by hiding in a refuge in late summer in the presence of a piscivore, and this caused Daphnia to spend more time feeding in the open water than when piscivores were absent. Thus, we conclude that, to explain patterns of habitat use in natural systems, it is of crucial importance that we recognize the existence of behavioral cascades

Moving beyond traditional measures – lessons from evaluating collaborative initiatives at Lund University

Over the last decade, universities and other institutions of higher education (HEIs) worldwide have witnessed an evolution to their role relative to society – with increasing attention to external engagement and expectations on societal impact. This has fostered an upswing in activity as research and innovation funding bodies and universities alike explore new approaches to working with external engagement, and led to questions regarding how to evaluate the societal impact of these efforts. Although there are examples of national frameworks to evaluate research impact, the large majority of countries and HEIs around theworld are still experimenting with approaches to evidence and assess their pathway to societal impact. This paper aims to contribute to evolving practice in this field by presenting lessons from the evaluation of a new strategic instrument (thematic collaboration initiatives) at Lund University (LU), Sweden.The evaluation of the strategic instrument “thematic collaboration initiatives” encompassed both initiative/operational and LU leadership/strategic levels. The approach to the evaluation combined traditional measures and processes, together with new indicators and evaluation approaches. The evaluation hasresulted in a better understanding of the range of activities and outputs that one can expect from such collaborative initiatives – informing the selection of measures to include in evaluation efforts. The evaluation also provided new insights on how universities can work with and use evaluation to guide thefurther development of the university’s approach to fostering external engagement. Participatory processes and facilitated reflection were very beneficial to draw out multiple perspectives and possible implicationsfor future development of the instrument

Tematiska samverkansinitiativ vid Lunds universitet - Resultat och reflektioner

Rapport som sammanfattar utvärderingen av den första generationen av tematiska samverkansinitiativ vid Lunds universitet 2017-2019

Effects of enrichment on simple aquatic food webs

Simple models, based on Lotka-Volterra types of interactions between predator and prey, predict that enrichment will have a destabilizing effect on populations and that equilibrium population densities will change at the top trophic level and every second level below. We experimentally tested these predictions in three aquatic food web configurations subjected to either high or low nutrient additions. The results were structured by viewing the systems as either food chains or webs and showed that trophic level biomass increased with enrichment, which contradicts food chain theory. However, within each trophic level, food web configuration affected the extent to which different functional groups responded to enrichment. By dividing trophic levels into functional groups, based on vulnerability to consumption, we were able to identify significant effects that were obscured when systems were viewed as food chains. The results support the prediction that invulnerable prey may stabilize trophic-level dynamics by replacing other, more vulnerable prey. Furthermore, the vulnerable prey, such as Daphnia and edible algae, responded as predicted by the paradox of enrichment hypothesis; that is, variability in population density increased with enrichment. Hence, by describing ecosystems as a matrix of food web interactions, and by recognizing the interplay between interspecific competition and predation, a more complete description of the ecosystem function was obtained compared to when species were placed into distinct trophic levels

The role of young-of-the-year fish in lake ecosystems

Food chain theory is based on consumption; that is, presupposing that the only important interaction between organisms is that they actually meet in an unstructured environment and that one of them is consumed. Recently, studies, including biomanipulation projects, have indicated that trophic interactions are more complex than predicted by food chain theory. In this thesis I examine the role of young-of-the- year (0+) fish in lake ecosystems, and I have performed studies in both experimental and whole lake systems, and used a new monitoring technique; horizontal echo sounding. The abundance of 0+ fish shows large fluctuations, within and among years, in our lakes, and most of our 0+ fish are zooplanktivorous during their first summer. Many fish species undergo ontogenetic niche shifts, that is they change their food preference and habitat use during their development fom fish larvae to adults. The change in 0+ fish abundance and in preferred prey implies that the impact of 0+ fish on zooplankton may vary considerably during summer. In this thesis I focus both on the direct predation impact of 0+ fish (of varying sizes and densities) on zooplankton and phytoplankton (the trophic cascade), and on the importance of ontogenetic changes in distribution and antipredator behaviour of 0+ fish (the behavioural cascade). I conclude that high abundances of 0+ fish may have an impact on a whole lake system, but that the impact on the plankton community is size dependent, and also dependent on ontogenetic behavioural decisions of 0+ fish. Thus, I show that to be able to predict the outcome of predator-prey interactions, we also have to consider the complex factors of ontogenetic development and movement of the organisms and their resources, and the antipredator behaviour of prey organisms

An evaluation of horizontal echo sounding as a method for behavioural studies of 0+fish in field experiments

A 120 kHz echo sounder, with two split-beam transducers, was used horizontally to monitor the behaviour of 0+ roach Rutilus rutilis, from June to August, in field enclosures. 0+ roach outside the vegetated area of the enclosures were registered both as schools and as single swimming fish. Combining echo counting and tracking with direct observation of echograms, an estimate of relative abundance of 0+ roach in the open water volume was obtained also. With this set up, intermediate sized field experiments studying 0+ fish, may be performed during the whole summer season. (C) 2001 The fisheries Society of the British Isles

Growth of larval and juvenile perch: the importance of diet and fish density

In August, growth rate of young-of-the-year (YOY) perch in lake enclosures could be explained by both YOY density and mean cladoceran biomass, suggesting that in a lake where YOY perch are dominant, growth may be density dependent in late summer and mediated through top-down control on daphnid biomass. In June, growth rate of YOY perch could not be fully explained by YOY density or by mean cladoceran biomass, suggesting that growth and survival during the first part of the summer is negatively affected by a diet of Bosmina and cyclopoid copepods only. The experiments also suggest why YOY perch have a slow growth and a low abundance in eutrophic lakes where small zooplankton dominate. The June experiment also indicated that growth of late larval or early juvenile perch improved when a larger cladoceran became available and was included in the diet. (C) 2000 The Fisheries Society of the British Isles

Environmentally controlled Daphnia spring increase with implications for sockeye salmon fry in lake washington, USA

In Lake Washington, juvenile sockeye salmon (Oncorhynchus nerka) strongly prefer Daphnia over other prey, switching uniformly to Daphnia when the threshold abundance of 0.4 Daphnia L-1 is achieved. Using long-term Lake Washington data (1978-2001) and fry trap data (1992-2001) from a major tributary, we examined the following: (i) factors that predict Daphnia pulicaria and Daphnia thorata increase to this threshold "switching" abundance, (ii) trends in Daphnia dynamics that may affect sockeye foraging and (iii) temporal correspondence of Daphnia increase and fry arrival. The winter abundance of D. pulicaria, in combination with basic parameters of spring conditions, was an important predictor of the date of D. pulicaria spring increase, indicating greater reliance on pelagic population dynamics (versus diapause hatch) than D. thorata exhibited. In addition, D. pulicaria was a more consistent prey than D. thorata, the latter exhibiting larger population fluctuations. Thus, recently increasing D. thorata prominence could decrease diet consistency for sockeye fry. Additionally, the timing of sockeye arrival to Lake Washington and Daphnia's increase to the switching threshold has become less concordant, so that fry in recent years have had to rely upon less profitable prey for longer periods. Long-term trends and species-specific differences in Daphnia phenology may affect fry through altering diet composition, with additional implications for other zooplankton withstanding greater predation pressure in Daphnia's absence. Recent decades of warming in Lake Washington are consistent with the warming of lakes worldwide, and complex phenological responses such as those reported here may be common as the climate continues to change